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From:   Daniel Palmer <daniel@0x0f.com>
Date:   Tue, 7 Sep 2021 23:32:20 +0900
Message-ID: <CAFr9PX=Oi-HJYUFBfJn4pHUSk=drf7otyx473hvq1UC5_gaTHQ@mail.gmail.com>
Subject: Re: [PATCH v2 4/5] ARM: Add basic support for Airoha EN7523 SoC
To:     Arnd Bergmann <arnd@arndb.de>
Cc:     Bert Vermeulen <bert@biot.com>,
        Russell King <linux@armlinux.org.uk>,
        Linus Walleij <linus.walleij@linaro.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Anshuman Khandual <anshuman.khandual@arm.com>,
        Marc Zyngier <maz@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        John Crispin <john@phrozen.org>,
        Ard Biesheuvel <ardb@kernel.org>,
        YiFei Zhu <yifeifz2@illinois.edu>,
        =?UTF-8?Q?Uwe_Kleine=2DK=C3=B6nig?= 
        <u.kleine-koenig@pengutronix.de>, Mike Rapoport <rppt@kernel.org>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        DTML <devicetree@vger.kernel.org>
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Hi Arnd,

On Tue, 7 Sept 2021 at 23:12, Arnd Bergmann <arnd@arndb.de> wrote:

> > I think the broken memory controller is still there so somehow I'd
> > need to get the heavy barrier to work in arm64. I haven't yet worked
> > out if that's even possible.
>I think I missed that part of the discussion, or I forgot about it already.
>What is the issue you are referring to here?

Sorry. I should have put a bit more context. This is for the SSD268G
not the original target of this series. But a similar situation.
The SSD268G (according to the decompiled device tree) is the same
hardware as the MSTAR_V7 chips but with a Cortex A53 instead of the
Cortex A7.
So it probably has the same memory controller as the MSTAR_V7 stuff
and that memory controller is not coherent so it needs the kernel to
make sure memory requests are flushed out to memory before DMA
happens[0]. For arm I fixed that with the heavy mb callback. With
arm64 I have no idea how to fix that.

I'm interested to see how this Airoha EN7523 series goes as if/when I
push anything for the SSD268G it'll probably only be for a 32bit
kernel.

0 - https://elixir.bootlin.com/linux/latest/source/arch/arm/mach-mstar/mstarv7.c#L61